EFFECT OF PLANES OF NUTRITION ON WINTERING PREGNANT BEEF COWS

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Abstract
During each of 4 years, 32 Shorthorn cows were individually fed at four levels during winter pregnancy and barn-nursing: (I) ad libitum corn silage plus 1.0 kg mixed hay per 100 kg initial body weight, daily; (II), (III) and (IV) approximately 80, 60 and 40%, respectively, of level-I intake. Half of the cows on each level received 0.45 kg linseed oilmeal (LOM) per head, daily, and half of both the LOM and no-LOM cows received supplemental vitamin A (84,000 IU per head, weekly). Considering only non-supplemented cows, levels of digestible protein and total digestible nutrients recommended by the National Research Council (U.S.) for winter-pregnancy feeding of beef cows were between levels I and II. During barn-nursing, even level-I cows fed LOM were substandard in relation to NRC recommendations.Average daily weight changes (ADWC) during both pregnancy and barn-nursing differed significantly (P < 0.05) and directly with decreasing levels of feed. ADWC’s on pasture also differed significantly (P < 0.05) but inversely with decreasing levels of winter feed. Aggregate yearly ADWC’s were significantly (P < 0.05) lower for level IV than for the other three levels. There was no significant (P > 0.05) interaction between LOM supplementation and level of feeding in relation to ADWC at any time. During pregnancy, LOM supplementation significantly (P < 0.05) decreased weight losses, whereas during the pasture season cows previously supplemented with LOM gained significantly (P < 0.05) less. There was no effect of LOM supplementation on ADWC during barn-nursing or aggregate yearly ADWC. No effect of vitamin A supplementation on ADWC or reproduction was noted.The results indicate that pregnant beef cows can lose substantial amounts of flesh during winter feeding and recover satisfactorily on pasture, although level-IV cows were at or below the limit for full weight recovery. Level-I cows were excessively fat throughout the experiment.